Acne.org Products
My brother is the same way. In my family, my dads side doesn't have good skin. My moms side has completely flawless skin. Really it's just genetics and whether your skin is acne prone or not. I'm the same way as you are. I eat icecream and I breakout the next day with a much oilier face. Two days ago my brother who has great skin literally took pizza and slapped it on his face and rubbed it in to prove a point. He didnt wash his face the entire day until he got into the shower. Even then he didn't wash his face. It truly is amazing how this stuff works. However, I personally believe all this skin care and healthy eating will make us healthier and stronger. I am certainly in better shape and more athletic than my brother even though I have acne. In the future our skin will be much healthier and younger looking once our acne just stops. It really is a weird concept to think about
Genetics, hormones...it's all in the blood really. Some people (like most of us here) breakout over a simple doughnut or as you mentioned, a cookie or two. Others, on the other hand, can eat a truckload of McDonalds and Oreos and not get a single pimple (like most of my friends). It's just something in everyone's DNA. Everyone is different. While we may be struggling with acne, some of your friends may have their own insecurities and/or flaws that may not be that noticeable to the naked eye. I don't know if I make myself clear enough with that example, but summarizing everything:
It's all genetics. DNA, family, skin type, all those factors are what causes acne.
Internal hormonal and oil gland receptor variables aside, someone basically has acne because of excess sebum production (oily skin), which potentially blocks pores, AND/OR hyperkeratinization, which means excess and uneven shedding of skin cells within the pore.
People with perfectly clear skin have the exact same P. acnes bacteria all over their face as you and I and anyone with severe acne. The difference is that someone with clear skin either has normalized keratinization or normalized sebum production or both. This would be essentially the result of genetically determined oil gland receptor sensitivity to stimulation by male sex hormones, though acne can also be influenced by diet, stress, and other factors in those who are acnegenic. Such a person with perfect skin simply does not have the underlying factors to create the kind of environment in the skin that encourages bacteria overpopulation within blocked pores as the pores themselves are not becoming blocked in the first place.
See these classic posts by Antony for further info:
http://www.acne.org/messageboard/topic/52997-antidote-in-sight/?p=606058
http://www.acne.org/messageboard/topic/51372-bums-and-acne/?p=595276
http://www.acne.org/messageboard/topic/53851-dry-skin-and-a-lot-of-pimples-on-forhead/?p=622044
http://www.acne.org/messageboard/topic/52246-oily-skin/?p=598563